The semiconductor integrated circuit (IC) industry has experienced rapid growth. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing ICs, and, for these advances to be realized, similar developments in IC manufacturing are needed.
As merely one example, metal device gates are incompatible with some conventional methods of forming passive devices (e.g., resistors, inductors, and capacitors). Many techniques for forming metal device gates include forming a polysilicon dummy gate early in the fabrication process. The polysilicon retains the gate shape during processing steps, such as annealing, that a metal gate might not survive. Eventually the dummy gate is etched away and the metal gate is formed. This is a concern for forming passive devices because some passive devices, particularly resistors, are conventionally formed using ion-implanted polysilicon. The etching to remove the dummy gate may not distinguish between the gate polysilicon and the polysilicon of the passive device. For this reason and others, although existing passive device structures and fabrication methods have been generally adequate, they have not proved entirely satisfactory in all respects.